The present disclosure relates to a laterally-activated mechanical pencil with an eraser-propelling mechanism.
The eraser-propelling mechanism makes it possible to extend or retract the eraser inside a barrel of the mechanical pencil, the barrel extending in a longitudinal direction.
To this end, the eraser-propelling mechanism generally comprises a tube carrying a helical cam and a translation guide cylinder making it possible to transform a rotation movement of the tube into a translation movement of the eraser in the longitudinal direction.
It should be understood that the guide cylinder is prevented from rotating relative to the barrel so that it is not rotated with the tube carrying the helical cam.
The guide cylinder is generally prevented from rotating either by mechanically clamping an end of the guide cylinder in the barrel and/or by cooperation between at least one groove and at least one rib located respectively at one end of the guide cylinder and on the barrel or vice versa.
Given the manufacturing tolerances on parts obtained by injection-molding plastics material for example, it may turn out to be difficult to achieve mechanical clamping and certain parts are scrapped.
In addition, it may also be difficult to carry out the dimensional controls of the rib and/or the groove in the barrel. Since the guide cylinder is generally inserted into the barrel via the end at which the groove or the rib is located, the rib or groove as the case may be of the barrel is of a dimension in the longitudinal direction that is relatively long (corresponding to the length of insertion of the guide cylinder in the barrel) and of a dimension in a circumferential direction that is relatively short.
In addition, that type of mechanical pencil is generally complicated to assembled since it is necessary to prevent certain parts from rotating about the longitudinal direction. Assembly is made even more complex by adding a side button for actuating a lead-propelling mechanism.
It is often necessary to index the parts in a circumferential or azimuth direction so as to be able to assemble all of the elements that make up the mechanical pencil.
Also, preventing the guide cylinder from rotating about the longitudinal direction and assembling the mechanical pencil with a side button may turn out to be difficult to perform in reliable and simple manner.